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    Re: Back In Hobby: Some Questions, Please
    From: Ken Muldrew
    Date: 2007 Apr 25, 17:10 -0600

    On 25 Apr 2007 at 18:17, Alexandre E Eremenko wrote:
    
    > Let me add few comments of my own.
    > I am really interested in this question whether
    > the best XIX century sextants (made for the Lunars)
    > were better than out modern ones.
    
    Peter Fidler in 1791, using a "brass sextant of five or six inches radius 
    made by Ramsden" reports the following two latitudes (among many celestial 
    observations, but I'm pretty sure that I know where he was when he made 
    these two).
    
    51�50'47" (actual latitude 51�02'55")
    52�21'37" (actual latitude 52�15'35")
    
    These are very bad but Fidler was a beginner at the time. Even still, I 
    have plotted his course on this trip and his lunars are not nearly as bad 
    as one would expect if his readings were this awful. I'll check tonight to 
    see if there is some better data to evaluate this small Ramsden sextant.
    
    David Thompson used a 10 inch radius brass sextant made by Dollond. His 
    latitudes at Rocky Mountain House from 1800 and 1801 were:
    
    52�21'29"
    52�21'27"
    52�21'35"
    52�21'32"
    
    The actual latitude is 52�21'20" but it should be remembered that Rocky 
    Mountain House is at an altitude of 3200' and Thompson did not account for 
    that in his calculation. So his sextant certainly seems pretty good at 
    this part of the arc. Recall that I posted his lunars from this same 
    position about 2 years ago and after correcting for the poor data in the 
    almanac, his sigma was about 14' in longitude for 13 observations. Not 
    that great, but it's hard to know how much was due to his sextant and how 
    much to observational errors.
    
    Ken Muldrew.
    
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